Photoepilation is a well-established technique for removing hair on the human skin and for temporarily preventing the growth of new hair. Before the actual epilation, the skin to be epilated is shaven. In the subsequent photoepilation step, the part of the skin that is to be epilated is exposed to intense light, typically in the form of a flash from a laser source, wherein the light is emitted through a treatment window. The treatment window is usually rectangular and has a cross section of a few square centimeters. In order to treat a larger area of the skin, the treatment window (and with it the entire treatment device) is moved over the skin in a stepwise manner, each step including the emission of a light flash, so that a different area of the skin is treated in each step. The wavelength of the laser light is chosen so as to be significantly absorbed by the hair sacks (follicles) in the skin. The absorbed radiation transforms into heat, thereby “inactivating” the follicles so that they will not produce new hair during a certain period after the treatment, typically about four weeks. After that period, the treatment has to be repeated for the skin to remain hair-free.
Although state-of-the art optical epilators use lasers as the light source, the light for photoepilation needs to be neither monochromatic nor coherent. The reasons for using lasers to generate the radiation are rather practical ones, such as a laser's small size, its limited frequency spectrum, high energy efficiency, high intensity and low cost. It is stressed that the present invention includes optical skin treatment devices in which the electromagnetic radiation used for treatment is generated by means other than a laser, for example by means of a broadband intense pulsed light source or flash lamp. It is further stressed that the present invention does not only include optical skin treatment devices for hair removal or hair growth reduction in general, but also includes optical skin treatment devices for other dermatological purposes such as, for example, skin rejuvenation, acne treatment, the treatment of psoriasis, etc.
The invention also applies to non-optical forms of surface treatment in which a surface, which is not necessarily skin, is to be treated in a stepwise manner via a treatment window. Examples of non-optical forms of surface treatment include applying RF energy, ultrasound energy, a liquid or paste, such as a lotion, oil or paint, to the surface via a treatment window, or plasma treatment via a treatment window, e.g. for sterilization or cleaning.
A problem of photoepilation and other optical skin treatment methods and devices is that the light incident on the skin does not immediately leave any visible mark on the skin. In fact, the effects of the exposure to light only manifest themselves in the reduced rate of hair growth or other dermatological result in the days or weeks following the treatment. Hence a lot of attention is needed during the treatment in order to expose every part of the skin that is to be epilated or otherwise treated, while avoiding exposing any part more than once. Indeed, a repeated treatment of the same area can be potentially harmful due to the additional amount of energy absorbed. In order to help the user in displacing the treatment window over the skin, state-of-the art optical skin treatment devices are provided with feedback means informing the user about the motion of the device and/or about the surface that has already been treated. The majority of these feedback means are designed to deliver optical or acoustic signals, for example, an LED that is illuminated when the skin treatment device has been moved by a distance corresponding to the width of the treatment window. Also in other forms of surface treatment (e.g. plasma surface treatment), the present invention will be especially useful when the effect of the treatment is not immediately visible to the naked eye.
U.S. Pat. No. 6,171,302 B1 discloses an apparatus and a method for synchronizing the activation of a light source with the position of a handpiece on a surface and for providing a substantially uniform exposure of a surface to light radiation. The handpiece, which is moved along the surface by an operator, includes a sensor for sensing the distance traversed by the handpiece on the surface. The sensor sends signals to a signal processing unit which calculates the distance traversed by the handpiece on the surface.
Providing the operator of a surface treatment device merely with optical or acoustic feedback signals has the disadvantage that the operator needs to interpret these signals correctly. Therefore, operating the device usually requires some training. In fact, photoepilation is nearly always performed by a professional therapist. Providing only optical feedback signals further has the disadvantage that the user would find it difficult to receive the optical signals when he or she were to apply the skin treatment device on parts of his (her) own body that he (she) cannot directly see, such as parts of his (her) back. Furthermore, state-of-the art feedback systems involve fairly complex electronics for evaluating the distance by which the treatment device has been moved along the surface to be treated and for triggering the feedback signal. The state-of-the-art feedback systems are rigidly integrated in the treatment device. However, it would be desirable to have user feedback means which can be flexibly adjusted to different operating parameters or to personal preferences of the user or the patient.
It is therefore an object of the present invention to provide a skin treatment device having a treatment window for treating skin through the treatment window and user guidance means for aiding a user of the skin treatment device in moving the treatment window along the skin in a stepwise manner, each moving step having a finite step width by which the treatment window is displaced, wherein the user guidance means are to be simple, easily modifiable, and to provide the user with easy-to-interpret feedback signals.
This object is achieved by the features of the independent claim. Further specifications and preferred embodiments of the invention are outlined in the dependent claims.